Thermochemistry Flashcards
Def. of Heat
- Energy transferred to the motion of atoms and molecules
- Represented as q or Delta H in Equations
Def. of Work
Energy transferred to the motion of objedcts
What’s Enthalpy’s equation?
Enthalpy = (sum of product’s heat capacity) - (sum of the reactant’s heat capacity)
-(each being multiplied by n, the number of moles)
What’s Hess’s law?
The total enthalpy change doesn’t depend on the pathway it takes, but on the initial and final state
What’s the three Hess Law Rules?
1) if you reverse a reaction, the sign of Delta H changes
2) if you multiply both sides by factor n, then Delta H must change by the factor n
3) when you add equations up, cross out what is the same n both sides of the reaction
What are the properties of a Endothermic reaction?
- Delta H > 0
- q is positive
- Heat is flowing into a system from its surrounding
- System gains heat as the surroundings cool down
- More energy in the products than the reactant
- Solid -> Liquid -> Gas (in equation)
What are the properties of a Exothermic reaction?
- Delta H < 0
- q is negative
- Heat is flowing out of the system into its surroundings
- System loses heat as the surrounding gains heat
- More energy in the reactant than the products
- Gas -> Liquid -> Solid (in equation)
What’s the heat capacity?
The amount of heat needed to increase the temp. of an object by 1 degree Celsius
Whats the standard enthalpy of formation?
- represented by (Delta Hf)
- is the heat change that results when one mole of a compound if formed from its elements at a pressure of 1 atm
- the SEF of any element in its most stable form is zero
ex. ) (Delta Hf)O2 = 0
Define a system
Def) the part of the universe on which you focus your attention
-together, the system and it’s surrounding constitute the universe
Define a surrounding
Def) includes everything else
-together, the system and it’s surrounding constitute the universe
